Evaluation of Japanese encephalitis virus DNA vaccine candidates in rhesus monkeys [Macaca mulatta]

We have previously described DNA vaccine candidates against Japanese encephalitis virus (JEV) that were immunogenic in mice. Present study was conducted to evaluate their immunogenicity in rhesus monkeys (Macaca mulatta) and compare it with the commercial mouse brain-derived, formalin-inactivated vaccine. Groups of four monkeys were immunized with either pMEa (expressing the anchored form of the envelope protein along with the pre-membrane protein of JEV) or pMEs (expressing the secretory form of the envelope protein along with pre-membrane protein of JEV) by intra-muscular (IM, using needle) or intra-dermal (ID, using gene gun) routes. Following primary immunization with 1mg plasmid DNA given IM, or 5 microg plasmid DNA given ID, the monkeys were boosted after 1 and 2 months with 0.5mg DNA given IM or 5 microg DNA given ID, and observed for a period of 6 months. After the second booster, most of the monkeys sero-converted and developed JEV neutralizing antibodies, albeit of low titer. Importantly however, following a sham challenge with the mouse brain-derived inactivated JEV vaccine given 6 months after immunization, the neutralizing antibody titers rose rapidly indicating a vigorous anamnestic response. Based on the JEV neutralizing antibody response following the vaccination and the extent of anamnestic response generated in the immunized monkeys, plasmid pMEa was superior to pMEs. This study indicates that the JEV candidate DNA vaccine is capable of generating protective levels of JEV neutralizing antibodies in rhesus monkeys and prime the immune system effectively against a subsequent exposure to JEV.